Branched-chain polyamine stabilizes RNA polymerase at elevated temperatures in hyperthermophiles

Polyamines of unique structure are integrated in Synura echinulata biosilica

Unicellar, biomineralizing algae like diatoms or Synurales are ubiquitous in various habitats all over the world and have an outstanding role in different biogeochemical cycles. They are well known for their elaborate nanopatterned cell structures consisting of amorphous biosilica, which is intracellularly synthesized. Special biomolecules assist in the silica formation. In particular, species-specific long-chain polyamines (LCPAs) are commonly found in diatom biosilica and seem to play a special role due to their ability to self-assemble and induce silica precipitation. In contrast to diatoms, no species from the order Synurales have been tested yet for the presence of LCPAs. Therefore, the present work deals with the analysis of Synura echinulata biosilica using a novel HPLC-HR-MS/MS method. The presence of unique LCPAs is shown, and their structure is elucidated via MS/MS experiments. LCPAs from S. echinulata are based on amino butyl repeat units-in contrast to all previously described LCPAs from other organisms, which are based on aminopropyl repeat units. The ubiquitous presence of LCPAs in biomineralizing species strongly indicates a general role of LCPAs in silica biomineralization.

Substrate Specificity of an Aminopropyltransferase and the Biosynthesis Pathway of Polyamines in the Hyperthermophilic Crenarchaeon Pyrobaculum calidifontis

The facultative anaerobic hyperthermophilic crenarchaeon Pyrobaculum calidifontis possesses norspermine (333), norspermidine (33), and spermidine (34) as intracellular polyamines (where the number in parentheses represents the number of methylene CH2 chain units between NH2, or NH). In this study, the polyamine biosynthesis pathway of P. calidifontis was predicted on the basis of the enzymatic properties and crystal structures of an aminopropyltransferase from P. calidifontis (Pc-SpeE). Pc-SpeE shared 75% amino acid identity with the thermospermine synthase from Pyrobaculum aerophilum, and recombinant Pc-SpeE could synthesize both thermospermine (334) and spermine (343) from spermidine and decarboxylated S-adenosyl methionine (dcSAM). Recombinant Pc-SpeE showed high enzymatic activity when aminopropylagmatine and norspermidine were used as substrates. By comparison, Pc-SpeE showed low affinity toward putrescine, and putrescine was not stably bound in its active site. Norspermidine was produced from thermospermine by oxidative degradation using a cell-free extract of P. calidifontis, whereas 1,3-diaminopropane (3) formation was not detected. These results suggest that thermospermine was mainly produced from arginine via agmatine, aminopropylagmatine, and spermidine. Norspermidine was produced from thermospermine by an unknown polyamine oxidase/dehydrogenase followed by norspermine formation by Pc-SpeE.